A vehicle in general utilizes clutches. For example, in order to switch between a two-wheel-drive (2WD) mode and a four-wheel-drive (4WD) mode, there may be a case where a clutch is interposed between two shafts and an actuator controls its connection-disconnection. As it is difficult to create sufficient thrust force by a single means, a cam mechanism may be combined therewith so as to multiply its output force.
For the purpose of realizing smooth operation of the cam mechanism, balls may be interposed between cam members. As the balls roll on cam faces that relatively rotates, the balls prominently reduce friction resistance. This reduces load on the actuator, but, since the balls merely establish point contacts on the cam faces, it is problematic to impose a great thrust force on the cam mechanism. Use of rollers in place of the balls may be a solution for this problem because the rollers can establish line contacts. Japanese Patent Application Laid-open No. 2005-201288 discloses a related art.